1. Field of the Invention
This invention relates to a vehicle collision sensor mounting device, and more particularly to a device for mounting a vehicle collision sensor which, at the time of a collision, applies a signal to an air bag and a pretensioner seat belt.
2. Related Art
A passenger restricting device such as an air bag and a pretensioner seat belt which, at the time of a collision, protects a passenger, needs a sensor and a decision circuit which detects the occurrence of a collision and applies a detection signal to the device. A variety of collision sensors are available--a coil spring type collision sensor, a role spring type collision sensor, a cylinder ball type collision sensor, and a semiconductor type collision sensor. Most of them have a decision circuit which determines whether or not it is a collision, a signal generating circuit, and an shock force detecting circuit as one unit.
In the case of a forward control (cab-over type) truck, the driving position is raised, so that the driver's head or chest is liable to hit the steering wheel. And the position of the steering wheel is liable to change more than in the case of an automobile. In addition, it, unlike an automobile, has no intermediate member such as a hood (bonnet), so that the shock is directly applied to the passenger. Furthermore, because of the state of installation of the steering wheel, it is difficult for the truck to have a full-bag type air bag.
Hence, in the case of the truck, although its main restraint system for the passenger is a pretensioner seat belt, it is necessary to install an air bag at a suitable part of the steering wheel as supplemental restraint system (SRS); that is, both the main and SRS are utilized for the protection of the passenger. In the prior art, a collision sensor for transmitting a detection signal to the air bag or pretensioner seat belt has been employed; however, it involves various problems which must be solved.
It is essential for the collision sensor to generate a signal immediately when a collision occurs. When the automobile is traveling on an uneven road, the collision sensor is greatly vibrated; however, the collision sensor should not determine the occurrence of a collision from it. In addition, it is also essential that its mounting section is hardly broken. Furthermore, the collision sensor should be high both in weather resistance and in water resistance. In addition, the maintenance, inspection, and replacement of the collision sensor should be simple. Moreover, the collision sensor can be installed with ease. In order to determine the position of the collision sensor which satisfies the above-described various requirements, the present inventor has installed the collision sensor at various parts of the vehicle, and measured the time required for the generation of an ignition signal for an inflator such as an air bag (hereinafter referred to as "TTF (Time to Fire)", when applicable). The results of measurement are as indicated in Table 1.
Table 1 indicates TTFs of the collision sensor at various positions compared with the TTF as a reference value, 1.00, which has been measured in the case where the collision sensor is installed on the pedal bracket. As shown in Table 1, where the collision sensor is installed at the front part of the engine hood under the seat, the center of the engine hood, and at the cab side sill, the ignition time is about 10 to 30% delayed. In the case where the collision sensor is installed at the steering shaft, the ignition time is delayed twice. On the other hand, when it is installed on the chassis frame, the ignition time occurs about 10% expedited. Heretofore, in many cases, the collision sensor is installed on the engine hood; however, this results in the following difficulty: Since the engine hood is low in rigidity, the time which elapses from the time instant that a collision occurs until the inflator operates is long, so that it is impossible to sufficiently restrict and protect the passenger. Of course, it is impossible to install the collision sensor on the steering shaft. On the other hand, in the case where the collision sensor is installed on the chassis frame, preferably the TTF is short. However, in this case, the collision sensor is exposed outside the vehicle body, and therefore it is low both in weather resistance and in water resistance. Thus, it has been found that the collision sensor should be installed on the pedal bracket.
On the other hand, a collision sensor has been disclosed by Japanese Patent Application (OPI) No. 330399/1993 (the term "OPI" as used herein means an "unexamined published application"). In the prior art, the collision sensor is mounted on the side panel (6) through an elastic rubber member (36). This is to damp the shock force, thereby to accurately output a collision detection signal at all times. However, the collision sensor mounting structure is disadvantageous in that the TTF is long.
In view of the foregoing, an object of the invention is to provide a vehicle collision sensor mounting device with which the TTF is short, and at the occurrence of a collision the passenger can be positively protected, and which is high in weather resistance and excellent in maintenance. On the other hand, the problem that the collision sensor generates an erroneous signal in response to an shock force which is not of a collision can be sufficiently eliminated by changing the circuit in the sensor or by the improvement of the decision criteria. The water resistance can be improved by the provision of a water-proof cover.